Evolutionary variation

Shifting sociality during primate ageing

Machanda, Z.P. & Rosati, A.G. (2020). Shifting sociality during primate ageing. Philosophical Transactions of the Royal Society B, 375: 20190620.

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Humans exhibit major age-related shifts in social relationships along with changes in social and emotional psychological processes that underpin these behavioral shifts. Does social aeging in nonhuman primates follow similar patterns, and if so, what are the ultimate evolutionary consequences of these social shifts? Here we synthesize empirical evidence for shifts in social behavior and underlying psychological processes across species. Focusing on three elements of social behavior and cognition that are important for humans—propensities to engage with others, the positive versus negative valence of these interactions, and capabilities to influence others, we find evidence for wide variation in the trajectories of these characteristics across primates. Based on this, we identify potential modulators of the primate social ageing process, including social organization, sex, and dominance status. Finally, we discuss how comparative research can contextualize human social ageing.

Logical inferences from visual and auditory information in ruffed lemurs and sifakas

De Petrillo, F. & Rosati, A.G. (2020). Logical inferences from visual and auditory information in ruffed lemurs and sifakas. Animal Behaviour, 164: 193-204

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Inference by exclusion, or the ability to select a correct course of action by systematically excluding other potential alternatives, is a form of logical inference that allow individuals to solve problems without complete information. Current comparative research shows that several bird, mammal, and primate species can find hidden food through inference by exclusion. Yet there is also wide variation in how successful different species are, as well kinds of sensory information they can use to do so. An important question is therefore why some species are better at engaging in logical inference than others. Here, we investigate the evolution of logical reasoning abilities by comparing two strepsirrhine primate species that vary in dietary ecology: frugivorous ruffed lemur (Varecia spp.) and folivorous Coquerel’s sifakas (Propithecus coquereli). Across two studies, we examined their abilities to locate food using direct information versus inference from exclusion and using both visual and auditory information. In Study 1, we assessed whether these lemurs could make inferences when full visual and auditory information about the two potential locations of food were provided. In Study 2, we then compared their ability to make direct inferences versus inferences by exclusion in both the visual and auditory domains. We found that both lemur species can use visual information to find food, but that only ruffed lemurs were also able to use auditory cues, mirroring differences in the complexity of their wild ecology. We further found that, unlike many anthropoid species tested to date, both strepsirrhine species failed to make inferences by exclusion. These results highlight the importance of natural history in understanding the evolution of logical inference, and help reconstruct the deeper phylogeny of primate cognition.


Ecological rationality: convergent decision-making in apes and capuchins

De Petrillo, F. & Rosati, A.G. (2019). Ecological rationality: convergent decision-making in apes and capuchins. Behavioural Processes, 164: 201-213.

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Humans and other animals appear to defy many principles of economic ‘rationality’ when making decisions. Here, we use an ecological rationality framework to examine patterns of decision-making across species to illu- minate the origins of these strategies. We argue that examples of convergent evolution—the independent emergence of similar traits in species facing similar environments—can provide a crucial test for evolutionary theories of decision-making. We first review theoretical work from evolutionary biology proposing that many economically-puzzling patterns of decision-making may be biologically adaptive when considering the en- vironment in which they are made. We then focus on convergence in ecology, behavior, and cognition of apes and capuchin monkeys as an example of how to apply this ecological framework across species. We review evidence that wild chimpanzees and capuchins, despite being distantly related, both exploit ecological niches characterized by costly extractive foraging and risky hunting behaviors. We then synthesize empirical studies comparing these species’ decision preferences. In fact, both capuchins and chimpanzees exhibit high tolerance for delays in inter-temporal choice tasks, as well as a preference for risky outcomes when making decisions under uncertainty. Moreover, these species exhibit convergent psychological mechanisms for choices, including emotional responses to decision outcomes and sensitivity to social context. Finally, we argue that identifying the evolutionary pressures driving the emergence of specific decision strategies can shed light into the adaptive nature of human economic preferences.


Heterochrony in chimpanzee and bonobo spatial memory development

Rosati, A.G. (2019). Heterochrony in chimpanzee and bonobo spatial memory development. American Journal of Physical Anthropology, 169: 302-321.

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Objectives: The emergence of human-unique cognitive abilities has been linked to our species’ extended juvenile period. Comparisons of cognitive development across species can provide new insights into the evolutionary mechanisms shaping cognition. This study examined the development of different components of spatial memory, cognitive mechanisms that support complex foraging, by comparing two species with similar life history that vary in wild ecology: bonobos (Pan paniscus) and chimpanzees (Pan troglodytes). Materials and Methods: Spatial memory development was assessed using a cross-sectional experimental design comparing apes ranging from infancy to adulthood. Study 1 tested 73 sanctuary-living apes on a task examining recall of a single location after a one-week delay, compared to an earlier session. Study 2 tested their ability to recall multiple locations within a complex environment. Study 3 examined a subset of individuals from Study 2 on a motivational control task. Results: In Study 1, younger bonobos and chimpanzees of all ages exhibited improved performance in the test session compared to their initial learning experience. Older bonobos, in contrast, did not exhibit a memory boost in performance after the delay. In Study 2, older chimpanzees exhibited an improved ability to recall multiple locations, whereas bonobos did not exhibit any age-related differences. In Study 3, both species were similarly motivated to search for food in the absence of memory demands. Discussion: These results indicate that closely-related species with similar life history characteristics can exhibit divergent patterns of cognitive development, and suggests a role of socioecological niche in shaping patterns of cognition in Pan.


Chimpanzee cognition and the roots of the human mind

Rosati, A.G. (2017). Chimpanzee cognition and the roots of the human mind. In: Chimpanzees and Human Evolution (M. Muller, R. Wrangham & D. Pilbeam, eds.). Cambridge: The Belknap Press of Harvard University Press, pp. 703-745.

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The origins of the human mind have been a puzzle ever since Darwin (1871, 1872). Despite striking continuities in the behavior of humans and nonhumans, our species also exhibits a suite of abilities that diverge from the rest of the animal kingdom: we create and utilize complex technology, pass cultural knowledge from generation to generation, and cooperate across numerous and diverse contexts. Why do humans exhibit these abilities, but other animals (mostly) do not? This is a fundamental question in biology, psychology, and philosophy. This puzzle involves two main parts. The first is concerned with identifying the psychological capacities that are unique to humans. This phylogenetic question can be addressed through careful comparisons of humans and other animals to pinpoint the cognitive traits that are likely derived in our species. The second is concerned with the function of these capacities, and the context in which they arose. This evolutionary question examines why, from an ultimate perspective, we evolved these specialized capacities in the first place. Solving these puzzles poses a special challenge because it is only possible to directly measure the cognition of living animals. The bodies of extinct species leave traces in the fossil record, and even some behavioral traits exhibit well-understood relationships with physical traits—such as relationships between dentition and dietary ecology, or mating system and sexual size dimorphism. These relationships provide important benchmarks when biologists infer the behavior of extinct species. Unfortunately, cognition does not fossilize, and neither do the brains that generate cognitive abilities. Even those features of neuroanatomy that do leave some trace in the fossil record—such as brain size or particular anatomical landmarks—are often related to the kinds of complex cognitive capacities potentially unique to humans in a coarse fashion. As such, identifying derived human cognitive traits requires reconstructing the mind of the last common ancestor of chimpanzees (Pan troglodytes), bonobos (Pan paniscus), and humans (Homo sapiens). This reconstruction then can be used to infer what cognitive characteristics have changed in the human lineage.

Ecological variation in cognition: Insights from bonobos and chimpanzees.

Rosati, A.G. (2017). Ecological variation in cognition: Insights from bonobos and chimpanzees. In: Bonobos: Unique in Mind, Brain and Behavior (B. Hare & S. Yamamoto, eds.). Oxford: Oxford University Press, pp. 157-170. 

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Bonobos and chimpanzees are closely related, yet they exhibit important differences in their wild socio-ecology. Whereas bonobos live in environments with less seasonal variation and more access to fallback foods, chimpanzees face more competition over spatially distributed, variable resources. This chapter argues that bonobo and chimpanzee cognition show psychological signatures of their divergent wild ecology. Current evidence shows that despite strong commonalities in many cognitive domains, apes express targeted differences in specific cognitive skills critical for wild foraging behaviours. In particular, bonobos exhibit less accurate spatial memory, reduced levels of patience and greater risk aversion than do chimpanzees. These results have implications for understanding the evolution of human cognition, as studies of apes are a critical tool for modelling the last common ancestor of humans with nonhuman apes. Linking comparative cognition to species’ natural foraging behaviour can begin to address the ultimate reason for why differences in cognition emerge across species.

Tolerant Barbary macaques maintain juvenile levels of social attention in old age, but despotic rhesus macaques do not

Rosati, A. G., & Santos, L. R. (2017). Tolerant Barbary macaques maintain juvenile levels of social attention in old age, but despotic rhesus macaques do not. Animal Behaviour, 130, 199-207.

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Complex social life is thought to be a major driver of complex cognition in primates, but few studies have directly tested the relationship between a given primate species’ social system and their social cognitive skills. We experimentally compared lifespan patterns of a foundational social cognitive skill (following another’s gaze) in tolerant Barbary macaques, Macaca sylvanus, and despotic rhesus macaques, Macaca mulatta. Semi-free-ranging monkeys (N = 80 individuals from each species) followed gaze more in test trials where an actor looked up compared to control trials. However, species differed in ontogenetic trajectories: both exhibited high rates of gaze following as juveniles, but rhesus monkeys exhibited declines in social attention with age, whereas Barbary macaques did not. This pattern indicates that developmental patterns of social attention vary with social tolerance, and that diversity in social behaviour can lead to differences in social cognition across primates.

Foraging cognition: Reviving the ecological intelligence hypothesis

Rosati, A. G. (2017). Foraging cognition: Reviving the ecological intelligence hypothesis. Trends in Cognitive Sciences, 21, 691-702.

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What are the origins of intelligent behavior? The demands associated with living in complex social groups have been the favored explanation for the evolution of primate cognition in general and human cognition in particular. However, recent comparative research indicates that ecological variation can also shape cognitive abilities. I synthesize the emerging evidence that ‘foraging cognition’ – skills used to exploit food resources, including spatial memory, decision-making, and inhibitory control – varies adaptively across primates. These findings provide a new framework for the evolution of human cognition, given our species’ dependence on costly, high-value food resources. Understanding the origins of the human mind will require an integrative theory accounting for how humans are unique in both our sociality and our ecology.

Decision making under uncertainty: preferences, biases, and choice

Rosati, A. G. (2017). Decision making under uncertainty: preferences, biases, and choice. In: APA Handbook of Comparative Psychology, Volume 2. (J. Call, ed.). American Psychological Association, pp. 329-357.

[PDF]  Abstract

Imagine a choice between two potential jobs: a position that is stable but intellectually mundane, or one that is more exciting but offers only short contract with some chance of renewal. These kinds of decisions can be agonizing because they involve uncertainty. While the first job option is a known quantity, the second job offers the possibility of being more fulfilling, but also the possibility of being let go in the near future. This uncertainty means that it is not possible to know the exact consequences of the decision in advance, making it difficult to judge the best course of action. Many important decisions involve this same sort of uncertainty—such as whether to invest in a new business, commit to a partner, or pursue a medical treatment. Yet uncertainty is not something only humans experience: it is pervasive in the natural world, and all animals must sometimes make decisions without complete information about the consequences of their actions. Consequently, illuminating how decision-makers respond to uncertainty is a problem of interest across both the social and biological sciences. This review will integrate theory from economics, psychology, and biology in order to understand the psychological mechanisms that animals use to make decisions under uncertainty, as well as what biological function these mechanisms might have. I further argue that comparative research is a powerful tool for understanding the nature of economic decision-making. Discovering that a particular decision-making pattern is widely shared across humans and other species—or conversely, unique to humans alone—can provide important insights about the types of experiences that engender these psychological processes.

The evolution of primate executive function: from response control to strategic decision-making

Rosati, A. G. (2017). The evolution of primate executive function: from response control to strategic decision-making. In: Evolution of Nervous Systems, Second Edition, Volume 3 (J. Kaas & L. Krubitzer, eds.). Amsterdam: Elsevier, pp. 423-437.

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Human cognition is permeated by self-control: the ability to engage in complex, goal-oriented behaviors rather than just react to the moment at hand. This chapter examines the evolutionary roots of these abilities by comparing the psychological capacities of humans and other primates. In fact, there is marked variation in how different primate species control their motoric responses to inhibit prepotent but ineffectual actions, engage in strategic decision-making to determine the best course of action, and learn and update their responses when contingencies change. Understanding how and why this variation emerged can shed light on the origins of human cognition.

Understanding human gaze

Bettle, R., & Rosati, A. G. (2016). Understanding human gaze. In: Encyclopedia of Evolutionary Psychological Science (T. Shackelford and V. Weekes-Shackelford, eds.). Springer, pp. 1-4.

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Social attention is a foundational component of human social behavior. Our ability to detect and think about the direction of other’s gaze involves the attribution of mental states to others and scaffolds the development of other complex cognitive skills. Gaze-following is also widespread among other primates, but the cognitive mechanisms underlying gaze-sensitive behaviors appear to differ across species. Understanding the evolutionary origins of human social attention capacities can reveal the roots of our species’ unique patterns of cognition and culture.

Uncovering the behavior and cognition of the earliest stone tool makers

Rosati, A. G. (2016). Uncovering the behavior and cognition of the earliest stone tool makers. Evolutionary Anthropology , 25, 269–270.

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In August 2016, the 13th Human Evolution Workshop at the Turkana Basin Institute (TBI) brought together a diverse group of scientists from archeology, paleontology, geology, primatology, cognition, and neuroscience. Organized by Sonia Harmand (Stony Brook and TBI), and Helene Roche (Centre National de la Recherche Scientifique) along with TBI director Lawrence Martin (Stony Brook), the workshop focused on the earliest evidence of stone knapping. This focus was spurred by the recent discovery of stone tools at the Lomekwi 3 site in Kenya, which have been dated to 3.3 Mya. It is suspected that these tools were produced by Kenyathropus platyops, the only hominin found in the region during that period. As delineated by Richard Leakey (Stony Brook and TBI), our task was to assess whether these tools represent a “cognitive Rubicon” —a fundamental transition in our lineage that demarcates the human species.

Reward type modulates human risk preferences

Rosati, A. G., & Hare, B. (2016). Reward type modulates human risk preferences. Evolution and Human Behavior, 37, 159–168.

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Money and biological rewards differ in many ways. Yet studies of human decision-making typically involve money, whereas nonhuman studies involve food. We therefore examined how context shifts human risk preferences to illuminate the evolution of decision-making. First, we assessed peoples’ risk preferences across food, prizes, and money in a task where individuals received real rewards and learned about payoffs through experience. We found that people were relatively more risk-seeking for both food and prizes compared to money—indicating that people may treat abstract reward markers differently from concrete rewards. Second, we compared human risk preferences for food with the performance of our closest phylogenetic relatives, chimpanzees (Pan troglodytes) and bonobos (Pan paniscus), in order to illuminate the evolutionary origins of human decision-making strategies. In fact, human and chimpanzees were both relatively more risk-seeking compared to bonobos. Finally, we investigated why people respond differently to money versus concrete rewards when making decisions. We found that people were more risk-prone when making decisions about money that was constrained as a store of value, compared to money that could be freely exchanged. This shows that people are sensitive to money’s usefulness as a store of value that can be used to acquire other types of rewards. Our results indicate that humans exhibit different preferences when making risky decisions about money versus food, an important consideration for comparative research. Furthermore, different psychological processes may underpin decisions about abstract rewards compared to concrete rewards.


Bonobos and chimpanzees exhibit human-like framing effects

Krupenye, C., Rosati, A. G., & Hare, B. (2015). Bonobos and chimpanzees exhibit human-like framing effects. Biology Letters, 11, 20140527.

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Humans exhibit framing effects when making choices, appraising decisions involving losses differently from those involving gains. To directly test for the evolutionary origin of this bias, we examined decision-making in humans’ closest living relatives: bonobos (Pan paniscus) and chimpanzees (Pan troglodytes). We presented the largest sample of non-humans to date (n = 40) with a simple task requiring minimal experience. Apes made choices between a ‘framed’ option that provided preferred food, and an alternative option that provided a constant amount of intermediately preferred food. In the gain condition, apes experienced a positive ‘gain’ event in which the framed option was initially presented as one piece of food but sometimes was augmented to two. In the loss condition, apes experienced a negative ‘loss’ event in which they initially saw two pieces but sometimes received only one. Both conditions provided equal pay-offs, but apes chose the framed option more often in the positive ‘gain’ frame. Moreover, male apes were more susceptible to framing than were females. These results suggest that some human economic biases are shared through common descent with other apes and highlight the importance of comparative work in understanding the origins of individual differences in human choice.


The evolutionary roots of human decision-making

Santos, L. R., & Rosati, A. G. (2015). The evolutionary roots of human decision-making. Annual Review of Psychology, 66, 321-347.

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Humans exhibit a suite of biases when making economic decisions. We review recent research on the origins of human decision making by examining whether similar choice biases are seen in nonhuman primates, our closest phylogenetic relatives. We propose that comparative studies can provide insight into four major questions about the nature of human choice biases that cannot be addressed by studies of our species alone. First, research with other primates can address the evolution of human choice biases and identify shared versus human-unique tendencies in decision making. Second, primate studies can constrain hypotheses about the psychological mechanisms underlying such biases. Third, comparisons of closely related species can identify when distinct mechanisms underlie related biases by examining evolutionary dissociations in choice strategies. Finally, comparative work can provide insight into the biological rationality of economically irrational preferences.